class  Ab{
	public static void main(String[] args) {
		int a=60
	    
		if(a>80){
		System.out.println("A");
		}else if(a>70){
		System.out.println("B");
		}else if(a>60){
		System.out.println("C");
		}else if(a<60 & a>0){
		System.out.println("D");
		}




	}
}
